EP3502638A1 - Pyroelectric sensor with electromagnetic shielding comprising a composite material - Google Patents

Abstract

A thermal pattern sensor (100) having an array of pyroelectric capacitors.The sensor further includes an electrically conductive electromagnetic shielding stage (140) located between a stage (130) comprising a pyroelectric material and a surface contact (181) of the sensor.The electromagnetic shielding stage (140) comprises a shielding layer (141) which comprises nanowires and / or nanotubes (1411) immersed in a surrounding medium (1412). Said nanowires and / or nanotubes (1411) have a thermal conductivity greater than that of said surrounding medium (1412) .A ratio between a pitch () of pixels of the pixel matrix and a thickness () of the shielding layer (141) is greater than or equal to 20. The invention provides both rapid heat transfer through the electromagnetic shielding stage, and weak lateral heat transfer from one pixel to the other of the electromagnetic shielding stage. sensor.

Description

TECHNICAL AREA

The invention relates to a thermal pattern sensor of the pyroelectric sensor type.

Such a sensor forms for example a papillary impression sensor, in particular a fingerprint sensor.

STATE OF THE PRIOR ART

A pyroelectric sensor exploits the pyroelectricity properties of a material, i.e. its ability to generate electrical charges in response to a temperature change.

Such a sensor comprises a matrix of pyroelectric capacitors, each forming a transducer for translating a temporal variation of temperature into an electrical signal.

Each pyroelectric capacitance comprises a pyroelectric material portion, disposed between a lower electrode and an upper electrode. One of the electrodes is set at a constant potential, and forms a reference electrode. The other electrode, called the charge collection electrode, collects pyroelectric charges generated by the pyroelectric material in response to a temperature change. The charge collection electrode is connected to a read circuit for measuring the amount of charge collected.

In operation, an object is pressed against a contact surface of the sensor.

The detection can simply exploit a temperature difference between this object and said contact surface. The sensor then performs passive type detection.

In the case of a fingerprint detection, the finger is pressed against the contact surface of the sensor.

At the level of the peaks of the impression, the finger is in direct physical contact with the sensor. A heat transfer between the skin and the contact surface of the sensor is carried out by conduction, which leads to a first time variation of temperature.

At the valleys of the footprint, the finger is not in direct physical contact with the sensor. Thermal transfer between the skin and the contact surface of the sensor takes place through the air. The air exhibits thermal insulating properties, which leads to a second, less important temporal variation in temperature.

The difference between these two temporal variations of temperature results in a difference between the signals measured by the pyroelectric capacitors, according to whether they are under a valley or under a crest of the footprint. The image of the impression then has a contrast that depends on this difference.

After a few seconds, the temperature of the finger and the temperature of the contact surface homogenize, and it is no longer possible to obtain a satisfactory contrast.

To overcome this drawback, heating means are added under the contact surface, to dissipate a certain amount of heat in each pixel of the sensor. The temperature variation measured in each pixel of the sensor then relates to the extent to which this amount of heat is removed from the pixel. This makes it possible to improve and conserve over time the contrast of an image acquired using said sensor. The sensor then performs an active type detection. Such a sensor is described for example in the patent application EP 2 385 486 .

In the case of a fingerprint detection, the temperature variation is important at the valleys of the footprint, where the heat is transferred to the finger only through the air, and lower at the level of the fingers. crests of the impression, where the heat is transferred efficiently to the finger, by conduction.

Whatever the type of detection used, a pyroelectric sensor advantageously comprises a so-called electromagnetic shielding stage, that is to say an electrically conductive stage, capable of being connected to a source of potential. constant, and forming an electromagnetic shield between an object to be imaged applied against the contact surface of the sensor, and the pyroelectric material portions of the sensor pixels. The electromagnetic shielding stage provides protection against electrostatic disturbances, especially around 50 Hz, avoiding the recovery of electromagnetic noise in the measurements made. It also protects the sensor against electrostatic discharges, brought by the contact of the object to be imaged against the contact surface of the sensor. In the case of a papillary impression sensor, it provides protection against electrostatic discharges caused by contact with the skin when the finger touches the contact surface of the sensor.

French patent application no. 16 57391, filed on July 29, 2016 describes an example of a pyroelectric sensor capable of performing active type detection, and comprising such an electromagnetic shielding stage. The electromagnetic shielding stage consists of a single layer of electrically conductive material.

The electromagnetic shielding stage extends between the contact surface of the sensor, and the pyroelectric material portions of the sensor pixels, preferably under a protective layer of the sensor.

In order not to hinder the heat exchange between an object to be imaged, pressed against said contact surface, and the pyroelectric material portions, the electromagnetic shielding stage must be able to transmit the heat.

However, if this stage consists of a layer of a material having too high thermal conductivity, there is a risk that the heat propagates laterally in the electromagnetic shielding stage, from one pixel to the other of the sensor. This phenomenon, called diathermy, prevents a thermal pattern on the contact surface from reproducing faithfully at the pyroelectric material portions.

Conversely, if this stage consists of a layer of a material having too low thermal conductivity, the heat exchanges through this stage are slowed down, also slowing the reading of the sensor pixels. This slower reading can be difficult, especially for large sensors.

An object of the present invention is to propose a solution for the electromagnetic shielding stage of a pyroelectric sensor to provide a high heat transfer rate, while limiting the heat transfer from one pixel to the other of the sensor.

STATEMENT OF THE INVENTION

• un étage d'électrodes de collecte de charges, comportant les électrodes de collecte de charge de chacun des pixels ; et
• un étage comprenant un matériau pyroélectrique, comportant les portions en matériau pyroélectrique de chacun des pixels.

This objective is achieved with a thermal pattern sensor comprising a matrix of pixels, each pixel comprising at least one pyroelectric capacitor, formed by a portion of pyroelectric material disposed between a so-called charge collection electrode and a so-called reference electrode, and the matrix of pixels comprising, superposed above a substrate:

• a charge collection electrode stage, comprising the charge collection electrodes of each of the pixels; and
• a stage comprising a pyroelectric material, comprising the pyroelectric material portions of each of the pixels.

The pixel array further comprises an electrically conductive electromagnetic shielding stage located between the stage comprising a pyroelectric material and a contact surface for applying thereon an object to be imaged.

According to the invention, the electromagnetic shielding stage comprises a shielding layer which comprises nanowires and / or nanotubes bathed in a medium called surrounding medium.

Said nanowires and / or nanotubes each consist of a material having a thermal conductivity greater than that of said surrounding medium.

In addition, a ratio between a pixel distribution pitch of the pixel matrix and a thickness of the shielding layer is greater than or equal to 20.

The material of the nanowires and / or nanotubes forms a good thermal conductor, in comparison with said surrounding medium. Preferably, this material has a thermal conductivity greater than a factor of at least 10, and even at least 20, to the thermal conductivity of said surrounding medium.

The material of the nanowires and / or nanotubes is, for example, metal or carbon.

In practice, the material of the nanowires and / or nanotubes is in addition an electrically conductive material.

The nanowires and / or nanotubes thus provide rapid heat transfer through the shielding layer, the heat propagating rapidly in the shielding layer through said nanowires and / or nanotubes.

In addition, the nanowires and / or nanotubes have in common to each have an elongate structure and reduced diameter. This structure makes it possible to limit heat transfers from one pixel to the other of the pixel matrix, when the heat passes through the shielding layer via the nanowires and / or nanotubes.

In addition, the thickness of the shielding layer, defined along an axis orthogonal to an upper or lower face of the substrate, is much less than a distribution pitch of the pixels of the pixel matrix.

This thickness is for example less than or equal to 1.5 microns, preferably less than or equal to 1.0 microns. This thickness is for example 600 nm.

The pixel pitch is in turn greater than or equal to 20 μm, and preferably greater than or equal to 50 μm.

Thus, a ratio between the pixel pitch and the thickness of the shielding layer is advantageously greater than or equal to 20, and even greater than or equal to 50.

Therefore, a nanowire or nanotube, even if it is only slightly inclined relative to the plane of the substrate, passes through the shielding layer over a large part of its thickness, without extending over many pixels of the pixel matrix. The high ratio between the pixel pitch and the thickness of the shielding layer thus makes it possible to limit heat transfer from one pixel to the other of the pixel matrix, while offering good heat transfer in the layer. shielding, in the direction of its thickness.

• des transferts thermiques rapides, selon un axe (Oz) orthogonal au plan du substrat; et
• une faible diffusion latérale de la chaleur, d'un pixel à l'autre du capteur.

The layer of shielding material, and therefore the electromagnetic shielding stage according to the invention, thus offer at the same time:

• rapid thermal transfers along an axis (Oz) orthogonal to the plane of the substrate; and
• a weak lateral diffusion of the heat, from one pixel to the other of the sensor.

Note that when a nanowire or nanotube slightly exceeds a neighboring pixel, this does not induce significant error in detection since most of the heat nevertheless extends into the right pixel. For example, if a nanowire or nanotube extends over 80% of its length on an initial pixel P1, and on 20% of its length on a neighboring pixel P2, the detection error will be only 20%.

It is also noted that, depending on the characteristic dimensions of the thermal pattern to be imaged, relative to the pixel size, it is possible to tolerate more or less significant overruns on neighboring pixels. In other words, if the characteristic dimensions of the thermal pattern to be imaged are of the order of several pixels, a nanowire or nanotube may protrude over neighboring pixels without this resulting in a critical detection error. In particular, an overshoot rate on the neighboring pixel is to be divided by the characteristic dimension of the thermal pattern, in pixels, to obtain the error rate in detection. Thus, it is not mandatory that the nanowires or nanotubes each have a length less than or equal to the width of a pixel.

In practice, the width of a valley or crest of a fingerprint corresponds to about 10 pixels of the sensor. Thus, if a nanowire or nanotube extends over 80% of its length on an initial pixel P1, and on 20% of its length on a neighboring pixel P2, the detection error will be only 2% (20% / 10).

If necessary, the electromagnetic shielding stage according to the invention can furthermore form the reference electrodes of the pixels of the pixel matrix. Alternatively, the reference electrodes extend into a sensor stage separate from the electromagnetic shielding stage.

Preferably, the material of the nanowires and / or nanotubes has a thermal conductivity at least ten times greater than that of said surrounding medium.

The shielding layer is advantageously made of a composite material, the composite material comprising said nanowires and / or nanotubes integrated in an agglomerate which forms said surrounding medium.

Preferably, the composite material comprises between 20% and 40% by weight of nanowires and / or nanotubes.

The binder may be an electrically insulating polymer matrix, the nanowires and / or nanotubes together forming a perforated network.

Alternatively, the binder may be an electrically conductive polymer matrix, the nanowires and / or nanotubes together forming a non-perforated network.

The nanowires and / or nanotubes advantageously each have a length strictly less than the pixel pitch of the pixel matrix.

The composite material may further comprise graphene particles.

In particular, the composite material may further comprise between 10% and 30% by weight of graphene particles.

In any event, the composite material preferably comprises between 30% and 40% by weight of binder, when the binder is electrically insulating. The composite material preferably comprises between 45% and 55% by weight of binder, when the binder is electrically conductive.

Preferably, the composite material comprises between 20% and 40% by weight of nanowires and / or nanotubes.

The electromagnetic shielding stage may further comprise studs comprising graphene or metal. Preferably, the height of the pads is greater than or equal to half the height of the shielding layer.

• chaque pixel comporte en outre un élément de chauffage, apte à chauffer par effet Joule la portion en matériau pyroélectrique dudit pixel ; et
• un étage de chauffage, comportant les éléments de chauffage de chacun des pixels, s'étend dans la matrice de pixels entre l'étage comprenant un matériau pyroélectrique et la surface de contact.

According to an advantageous embodiment:

• each pixel further comprises a heating element, able to heat by Joule effect the pyroelectric material portion of said pixel; and
• a heating stage, comprising the heating elements of each of the pixels, extends in the matrix of pixels between the stage comprising a pyroelectric material and the contact surface.

• les éléments de chauffage d'une même ligne de pixels sont formés ensemble d'un seul tenant, en une même bande de chauffage ;
• les électrodes de collecte de charges d'une même colonne de pixels sont formées ensemble d'un seul tenant, en une même macro-électrode de collecte de charges ; et
• l'étage de blindage électromagnétique comprend en outre une matrice de plots comportant du graphène ou du métal, chaque plot s'étendant à travers une région d'intersection entre une projection d'une bande de chauffage et une projection d'une macro-électrode de collecte de charges, lesdites projections étant des projections orthogonales dans un plan parallèle à une face supérieure ou inférieure du substrat.

Preferably, according to this advantageous embodiment:

• the heating elements of the same pixel line are formed together in one piece, in the same heating band;
• the charge collection electrodes of the same column of pixels are formed together in one piece, in the same macro-charge collection electrode; and
• the electromagnetic shielding stage further comprises a matrix of studs comprising graphene or metal, each stud extending through an intersection region between a projection of a heating band and a projection of a macro-electrode for collecting charges, said projections being orthogonal projections in a plane parallel to an upper or lower face of the substrate.

• l'étage d'électrodes de collecte de charges ;
• l'étage comprenant un matériau pyroélectrique ;
• l'étage de blindage électromagnétique, formant en outre les électrodes de référence des pixels de la matrice de pixels ;
• une couche d'isolation électrique ; et
• l'étage de chauffage.

The matrix of pixels may comprise, superimposed:

• the charge collection electrode stage;
• the stage comprising a pyroelectric material;
• the electromagnetic shielding stage, further forming the reference electrodes of the pixels of the pixel array;
• an electrical insulation layer; and
• the heating stage.

• l'étage d'électrodes de collecte de charges ;
• l'étage comprenant un matériau pyroélectrique ;
• l'étage de chauffage, les éléments de chauffage formant en outre les électrodes de référence des pixels de la matrice de pixels ;
• une couche d'isolation électrique ; et
• l'étage de blindage électromagnétique.

In a variant, the matrix of pixels may comprise, superimposed:

• the charge collection electrode stage;
• the stage comprising a pyroelectric material;
• the heating stage, the heating elements further forming the reference electrodes of the pixels of the pixel matrix;
• an electrical insulation layer; and
• the electromagnetic shielding stage.

The invention also relates to a method for manufacturing the pixel matrix of a thermal pattern sensor according to the invention, in which a step of producing the electromagnetic shielding stage comprises a deposit of an ink comprising, in suspension in a solvent, said nanowires and / or nanotubes.

BRIEF DESCRIPTION OF THE DRAWINGS

• les figures 1A et 1B illustrent de manière schématique un premier mode de réalisation d'un capteur de motifs thermiques selon l'invention ;
• la figure 1C illustre une variante du mode de réalisation des figures 1A et 1B ;
• les figures 2A et 2B illustrent de manière schématique un deuxième mode de réalisation d'un capteur de motifs thermiques selon l'invention ;
• la figure 2C illustre une variante du mode de réalisation des figures 2A et 2B ;
• les figures 3A et 3B illustrent de manière schématique un troisième mode de réalisation d'un capteur de motifs thermiques selon l'invention ; et
• la figure 3C illustre une variante du mode de réalisation des figures 3A et 3B.

The present invention will be better understood on reading the description of exemplary embodiments given purely by way of indication and in no way limiting, with reference to the appended drawings in which:

• the Figures 1A and 1B schematically illustrate a first embodiment of a thermal pattern sensor according to the invention;
• the figure 1C illustrates a variant of the embodiment of the Figures 1A and 1B ;
• the Figures 2A and 2B schematically illustrate a second embodiment of a thermal pattern sensor according to the invention;
• the Figure 2C illustrates a variant of the embodiment of the Figures 2A and 2B ;
• the Figures 3A and 3B schematically illustrate a third embodiment of a thermal pattern sensor according to the invention; and
• the figure 3C illustrates a variant of the embodiment of the Figures 3A and 3B .

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

For greater clarity, the figures show the axes (Ox), (Oy) and / or (Oz) of an orthonormal coordinate system. The scales are not respected in the figures, in particular the thicknesses of each of the layers and / or stages.

The Figures 1A and 1B schematically illustrate a first embodiment of a thermal pattern sensor 100 according to the invention. The Figure 1A is a schematic view from above, in a plane parallel to the plane (xOy). The Figure 1B is a sectional view in a plane AA 'parallel to the plane (yOz).

• un étage 120 nommé étage d'électrodes de collecte de charges ;
• un étage 130 comprenant un matériau pyroélectrique ;
• un étage 140 de blindage électromagnétique ;
• une couche d'isolation électrique 160 ;
• un étage de chauffage 170 ; et
• une couche de protection 180 (optionnelle).

The thermal pattern sensor 100 comprises, superimposed above a substrate 110, along the axis (Oz) orthogonal to an upper or lower face of said substrate:

• a stage 120 named stage of charge collection electrodes;
• a stage 130 comprising a pyroelectric material;
• a stage 140 of electromagnetic shielding;
• an electrical insulation layer 160;
• a heating stage 170; and
• a protective layer 180 (optional).

This stack forms a matrix of pixels, in which each pixel comprises at least one pyroelectric capacitance, formed by a pyroelectric material portion disposed between a charge collection electrode, and a reference electrode. In this embodiment, the electromagnetic shielding stage 140 also forms a reference electrode common to all the pixels of the pixel array.

The substrate 110 is for example made of glass, of silicon, in a pastic such as poly (ethylene terephthalate) (PET), poly (ethylene naphthalate) (PEN), polyimide (Kapton film), etc. It is preferably a flexible substrate, for example a polyimide substrate of 5 microns to 10 microns thick, or a plastic such as PET.

It has an upper face and a lower face parallel to each other, and parallel to the plane (xOy). In the following, the plane of the substrate designates a plane parallel to these lower and upper faces.

The charge collection electrode stage 120 here comprises an array of charge collection electrodes 121 arranged in rows and columns along the axes (Ox) and (Oy).

The charge collection electrodes are made of a metal such as gold or silver, or any other electrically conductive material.

They are distributed along the axes (Ox) and (Oy), in a distribution pitch less than or equal to 150 microns. The distribution pitch is for example about 80 microns (a resolution of 320 dpi), or 90 microns. As a variant, the distribution pitch may be 50.8 μm (ie a resolution of 500 dpi).

Each of the charge collection electrodes 121 delimits, here laterally, the pyroelectric capacitance 10 of one of the pixels of the pixel matrix (see FIG. Figure 1B ).

The stage 130 comprising a pyroelectric material is constituted here of a full layer comprising polyvinylidene fluoride (PVDF) or one of its derivatives (in particular the copolymer PVDF-TrFE, TrFE for tri-fluoro-ethylene) .

Alternatively, the layer 130 comprises aluminum nitride (AIN), barium titanate (BaTiO ₃ ), lead Titano-Zirconate (PZT), or any other pyroelectric material.

The layer 130 extends in one piece, and without opening, covering all of the charge collection electrodes 121 of the stage 120.

Each portion of the layer 130, facing a charge collection electrode 121, forms the pyroelectric material portion of a pixel of the pixel matrix.

The electromagnetic shielding stage 140 forms an electrically conductive stage, comprising a shielding layer made of a composite material described hereinafter.

It is able to be connected to a source of constant potential, for example to ground.

The stage 140 preferably extends in one piece, and without opening, above all the charge collection electrodes 121 of the stage 120, that is to say passing through all the pixels of the pixel matrix.

Here, the stage 140 also forms a reference electrode, common to all the pixels of the pixel matrix. In other words, each portion of the stage 140, located opposite a charge collection electrode 121, forms the reference electrode of a pixel of the pixel matrix.

The electrical insulation layer 160 is made of a dielectric material, for example polyimide. It preferably has a thickness less than 5 microns, for example equal to 1 micron.

According to the embodiment of Figures 1A and 1B each pixel of the pixel matrix further comprises a heating element, the heating elements extending here in the heating stage 170.

Here, the heating elements of the same row of pixels are electrically interconnected to form a heating band 171. The heating strips 171 are adapted to receive a heating current, to provide a heating effect Joule, of to perform an active type detection. They are preferably made of a metal, for example gold or silver.

The protective layer 180 forms the outermost layer of the sensor. It makes it possible to limit the wear associated with repeated contacts with an object to be imaged, in particular with the skin. The protective layer 180 is for example a layer of DLC (Diamond Like Carbon), resin, polyimide, etc. It generally has a thickness of between a few micrometers and 25 microns.

An upper surface 181 of the protective layer 180, on the opposite side of the substrate 110, forms a contact surface of the thermal pattern sensor 100. In operation, an object to be imaged such as a papillary impression is applied against said contact surface 181, so as to perform heat exchange with the stage comprising a pyroelectric material.

According to the invention, the electromagnetic shielding stage 140 comprises a shielding layer 141, made of composite material, covering all of the charge collection electrodes 121 of the stage 120.

A composite material is composed of at least two components, assembled together into a heterogeneous structure. These constituents remain separate and separated in the composite material. They each have different physical or chemical properties. The composite material has properties that each of the constituents, taken alone, does not have. It can be considered that it combines, or average, physical or chemical properties of its various constituents.

• des structures allongées électriquement conductrices, ici des nanofils métalliques 1411 ; et
• un agglomérant 1412, nommé également liant, ou matrice, dans lequel sont noyés les nanofils métalliques 1411.

The composite material is constituted here by:

• elongated electrically conductive structures, here metal nanowires 1411; and
• a binder 1412, also called binder, or matrix, in which are embedded the metal nanowires 1411.

Here, the electromagnetic shielding stage 140 consists entirely of said shielding layer 141.

The binder 1412 forms a surrounding medium in which the metal nanowires 1411 extend.

The binder 1412 generally consists of a polymeric material called a polymer matrix. It ensures the cohesion of the metal nanowires 1411, and their holding in position in the shielding layer, fixed relative to each other. It forms a surrounding environment

The metal nanowires 1411 are physically isolated from each other by portions of the binder 1412, except, where appropriate, at one or more point (s) of contact between two neighboring nanowires. The density of said contact points increases with the density of metal nanowires 1411 in the composite material.

The arrangement of the nanowires shown in the figures is purely illustrative, and in no way limits the scope of the invention.

• l'agglomérant 1412 forme un mauvais conducteur thermique ; et
• les nanofils métalliques 1411 sont constitués d'un matériau formant un bon conducteur thermique.

According to the invention:

• the binder 1412 forms a bad thermal conductor; and
• the metal nanowires 1411 consist of a material forming a good thermal conductor.

Thus, the heat circulates rapidly in the shielding layer, mainly via metal nanowires 1411.

In addition, the metal nanowires 1411 are generally thermally isolated from each other by portions of the binder 1412. The thermal insulation between the metal nanowires 1411 decreases, as the density of nanowires in the composite material increases.

The thickness H of the shielding layer 141 of composite material is defined along the axis (Oz), orthogonal to the plane of the substrate.

The pitch P pixel is defined in a plane parallel to the plane of the substrate.

Preferably, the pixels of the pixel matrix are distributed according to a square mesh matrix having the same pitch P along the axes (Ox) and (Oy). If the pixels are distributed according to a mesh defined by several steps, for example a rectangular mesh defined by a step according to (Ox) and a step according to (Oy), consider the smallest of these steps.

The pixel pitch P is at least 20 times greater than the thickness H, and even at least 50 times greater than the thickness H.

Preferably, the thickness H is less than 1 μm, for example equal to 0.6 μm or 0.5 μm.

The pixel pitch P corresponds to the distribution pitch of the charge collection electrodes, for example 50.8 μm or 80 μm, or preferably 90 μm.

The heat flows in the shielding layer 141 of composite material, mainly via the metal nanowires 1411.

• des transferts thermiques rapides à travers la couche de blindage 141, selon l'axe (Oz) ; et
• des transferts thermiques limités d'un pixel à l'autre de la matrice de pixels, au niveau de la couche de blindage 141.

Thanks in particular to the high ratio between the pixel pitch P, according to (Ox), respectively (Oy), and the thickness H of the shielding layer 141, according to (Oz), it is possible to obtain at the same time:

• rapid thermal transfers through the shielding layer 141, along the axis (Oz); and
• limited heat transfer from one pixel to the other of the matrix of pixels, at the level of the shielding layer 141.

The metal nanowires 1411 consist of a material having a thermal conductivity greater than or equal to 100 Wm ^-1 K ^-1 .

The metal nanowires 1411 comprise, for example, a metal such as silver, gold, copper, aluminum, etc. They are for example silver, with a thermal conductivity of between 400 and 429 Wm ^-1 K ^-1 (depending on a level of impurities of the silver metal).

The binder 1412 is preferably made of a material having a thermal conductivity less than or equal to 10 Wm ^-1 K ^-1 .

Even more preferably, it consists of a material having a thermal conductivity less than or equal to 1 Wm ^-1 K ^-1 .

It is for example in PEDOT: PSS (mixture of poly (3,4-ethylenedioxythiophene) (PEDOT) and poly (styrene sulfonate) sodium (PSS)), having a thermal conductivity of 0.3 Wm ^-1 K ^-1 .

In any event, the thermal conductivity of the material forming the metal nanowires 1411 is preferably at least ten times greater than that of the binder 1412.

The shielding layer 141 forms an electrically conductive layer. In particular, it must be able to be supplied with voltage, which does not require the conduction of a current throughout said layer.

Several solutions make it possible to obtain this property of electrical conduction.

A first solution is to use an electrically insulating binder 1412 combined with a high density of metal nanowires 1411.

Nanowires 1412, since they consist of metal, are electrically conductive. In other words, they consist of a material having a low electrical resistivity, for example about 16.10 ^-9 Ω.m for silver, or 23.10 ^-9 Ω.m for gold.

Since the binder is electrically insulating, the electrical conduction is provided by the metal nanowires 1412, which together form a so-called perforated network. In other words, couples of two points belonging to two opposite edges of the shielding layer can be connected together by a continuous sequence of nanowires, each in direct physical contact with the next.

The electrically insulating binder 1412 is, for example, a polyvinylpyrrolidone (PVP), or poly (methyl methacrylate) (PMMA), or polystyrene (PS), or CYTOP ™ (amorphous fluoropolymer) polymer matrix.

This first solution gives access to a wide range of materials to form the binder, and a wide range of inks to achieve the composite material shielding layer (see below).

According to a second solution, the binder 1412 is electrically conductive.

The binder can be in PEDOT: PSS, or in PEDOT, of electrical resistivity equal to 50000.10 ^-9 Ω.m.

PEDOT and PEDOT: PSS have the advantage that they can be deposited without the need for a controlled atmosphere. However, other materials are not such as poly (p-phenylene sulfide), polypyrrole (PPY), polythiophene (PT), polyacetylene (PAC), polyaniline (PAni), melanin, organic dielectrics, etc.

The electrical resistivity of the material forming the agglomerator 1412 can be much greater than that of a metal, for example greater than or equal to 10000 × 10 ^-9 Ω.m, since the composite material shielding layer is intended to withstand weak currents only. .

In this second solution, the metal nanowires 1412 can together form a non-perforated network.

This second solution makes it possible to use a composite material having a low density of metal nanowires, which limits heat transfer from one pixel to the other of the pixel matrix, via one or more nanowires ( s).

The metal nanowires 1411 preferably each have a diameter of between 10 nm and 300 nm, more particularly between 10 nm and 100 nm. Such diameters avoid disturbing layers deposited above the shielding layer on the opposite side of the substrate.

Preferably, the metal nanowires 1411 each have a length strictly less than the pixel pitch of the pixel matrix. This length is generally between 5 microns and 100 microns, depending on the size of the pixel pitch.

In any case, the density of metal nanowires 1411 is preferably between 20% and 40% by weight of the composite material. Such a proportion limits the lateral diffusion of heat via metal nanowires.

With an electrically conductive binder 1412, the composite material 141 preferably comprises between 20% and 30% by weight of metal nanowires 1411.

With an electrically insulating binder 1412, the composite material 141 preferably comprises between 30% and 40% by weight of metal nanowires 1411, for example 35% by weight.

Preferably, the shielding layer 141, made of composite material, has between 200 and 300 nanowires / mm ² , for example between 220 and 260 nanowires / mm ² .

In practice, two nanowires maximum extend in the shielding layer 141, in the direction of the thickness.

The first embodiment as described above also has the advantage of not requiring special alignment of the electromagnetic shielding stage relative to the pixels of the pixel matrix.

The figure 1C illustrates, in a sectional view in a plane parallel to the plane (yOz), a variant 100 'of the embodiment of the Figures 1A and 1B .

This variant does not differ from that of Figures 1A and 1B in that the composite material of the shielding layer 141 'further comprises graphene particles 1413, distributed with the metal nanowires 1411 in the binder 1412.

Graphene is a two-dimensional material whose stack constitutes graphite, graphite being a crystallized form of carbon. Graphene is thermally and electrically conductive.

The graphene particles denote planar clusters in graphene, distributed here in the shielding layer, and oriented in planes parallel to the plane of the substrate.

Graphene particles have a planar geometry. They have a section width of between 1 micron and 10 microns, and a thickness between a few nanometers and 100 nm.

Preferably, the graphene particles are made using a printable ink based on graphene, for example Vor-ink ™ ink. The graphene particles, distributed in the composite material, make it possible to direct the temperature locally along the axis (Oz). Thermal transfer is all the more effective as the section of the graphene particles is important.

The graphene particles, of large section and reduced thickness, are therefore complementary to metal nanowires, of small section and of great length.

The graphene particles also have the advantage of making a good interface with the layer 130 comprising a pyroelectric material.

They can further establish electrical and thermal contacts between neighboring nanowires.

The composite material comprises for example between 10% and 30% by weight of graphene particles.

Depending on whether the binder 1412 is electrically conductive or not, and depending on the density of metal nanowires, the preferred amount of graphene particles varies.

With an electrically conductive binder 1412, the composite material comprises for example between 10% and 20% by weight of graphene particles. It comprises, for example, 35% by weight of metal nanowires, 50% by weight of agglomerator, and 15% by weight of graphene particles, or even 25% by weight of metal nanowires, 50% by weight of agglomerant, and % by weight of graphene particles.

With an electrically insulating binder 1412, the composite material comprises for example between 20% and 30% by weight of graphene particles. It comprises, for example, 35% by weight of metal nanowires, 40% by weight of binder, and 25% by weight of graphene particles, or even 25% by weight of metal nanowires, 40% by weight of agglomerant, and % by weight of graphene particles.

The Figures 2A and 2B schematically illustrate a second embodiment of a thermal pattern sensor 200 according to the invention. The Figure 2A is a schematic view from above (in transparency), in a plane parallel to the plane (xOy). The Figure 2B is a sectional view in a plane BB 'parallel to the plane (yOz).

This second embodiment differs from the embodiment of the Figures 1A and 1B that the electromagnetic shielding stage 240 further comprises pads 242, each pad being constituted by a thermally conductive material such as graphene or a metal.

The pads 242 are entirely in the shielding layer of composite material.

• une sous-couche inférieure, située du côté du substrat 210, et recevant les plots 242 entourés de matériau composite ; et
• une sous-couche supérieure, située au-dessus de la sous-couche inférieure, et entièrement constituée du matériau composite.

Preferably, they penetrate into the composite material shielding layer, from its lower face, located on the side of the substrate 210. The composite material then extends between the pads, and above the pads on the side opposite the substrate. 210. It is then possible to identify, in the electromagnetic shielding stage 240:

• a lower sub-layer, located on the side of the substrate 210, and receiving the pads 242 surrounded by composite material; and
• an upper sub-layer, located above the lower sub-layer, and made entirely of the composite material.

Here, the electromagnetic shielding stage 240 consists of the shielding layer of composite material and said pads 242.

Here, the pads 242 are distributed regularly, in rows and in columns, so that each pixel of the pixel matrix comprises a single and single pad 242. In other words, each pixel of the pixel matrix comprises a portion of the electromagnetic shielding stage 240, and said portion receives a single pad 242.

Preferably, the geometric center of a pad 242 and the geometric center of the associated pixel together define an axis parallel to the axis (Oz).

• un diamètre D (dimension dans un plan parallèle au plan du substrat 210) ; et
• une hauteur h (dimension selon l'axe (Oz), orthogonal au plan du substrat 210).

The studs 242 have for example a cylinder shape of revolution, presenting:

• a diameter D (dimension in a plane parallel to the plane of the substrate 210); and
• a height h (dimension along the axis (Oz), orthogonal to the plane of the substrate 210).

Here, each stud 242 sinks, along the axis (Oz) orthogonal to the plane of the substrate, on less than half the thickness H of the shielding layer of composite material.

The diameter D is less than the pixel pitch of the pixel matrix, for example two times smaller than the pitch of the pixel matrix. This diameter D is for example 10 μm and 100 μm, preferably between 50 μm and 60 μm. (The studs 242 are undersized on the Figures 2A and 2B .)

In any case, the pads 242 are physically isolated from each other, without direct physical contact between them.

The studs 242 cooperate with the metal nanowires of the composite material, to promote heat transfer along the axis (Oz), in the electromagnetic shielding stage 240, and limit transverse heat transfer in said stage 240, in planes (xOy ).

Preferably, the pads are made using a printable ink, for example a graphene-based ink, for graphene pads, or a metal ink, for pads comprising a metal.

The conditions stated above, relating to the thickness H of the composite material shielding layer also apply in this second embodiment, wherein pads are integrated in said shielding layer.

The invention is not limited to studs 242 in the form of a cylinder of revolution.

They may have a shape comprising a cylindrical central body vertically framed between a hat and a concave foot. The diameter of a pad then corresponds to the diameter of its central cylindrical body.

According to other variants, not shown, the studs have non-circular sections in planes parallel to the plane of the substrate, for example square or rectangular sections, side included for example between 10 microns and 40 microns.

Where appropriate, it is possible to define the diameter of a stud as being the greatest length measured along a rectilinear axis, on this stud, in a plane parallel to the plane of the substrate.

The pads are distinguished from any graphene particles of the composite material, in particular by their dimensions: their diameter is greater than 10 microns.

The Figure 2C illustrates, in a sectional view in a plane parallel to the plane (yOz), a variant 200 'of the embodiment of the Figures 2A and 2B .

This variant does not differ from that of Figures 2A and 2B in that the composite material further comprises graphene particles 2413, distributed with the metal nanowires 2411 in the binder 2412.

The Figures 3A and 3B schematically illustrate a third embodiment of a thermal pattern sensor 300 according to the invention. The figure 3A is a schematic view from above, in a plane parallel to the plane (xOy). The figure 3B is a sectional view in a plane CC 'parallel to the plane (xOz).

In this third embodiment, each pixel comprises a heating element, and these heating elements are used for passive addressing of the sensor pixels.

The heating elements of the same pixel line are electrically interconnected to form a heating band 371. Each heating band 371 is configured to be activated independently of the other heating strips. In other words, the heating elements of the pixels of the same pixel line are able to heat the pyroelectric material portions of the pixels of said line, independently of the heating elements of the pixels of the other lines. The heating strips 371 each have a first end, adapted to be connected to a non-zero electrical potential, and a second end, preferably connected to ground. Here, the second ends of all the heating strips are interconnected via a conductive portion 373.

In addition, the charge collection electrodes of the same column of pixels are electrically connected together to form a charge collection macro-electrode 321. Each charge collection macro-electrode 321 is formed by an electrically conductive strip, in contact with the pyroelectric material portions of the pixels of said column of pixels, and distinct from the electrically conductive bands forming the charge collection macroelectrodes of the other columns of pixels.

Each macro-charge collection electrode 321 makes it possible to measure the sum of the pyroelectric charges generated in the same column of pixels. If only one of the heating bands 371 is activated at each instant, in each column of pixels there is only one pixel that generates pyroelectric charges. The pyroelectric charges collected by the macro charge collection electrode 321 then relate to this single pixel. Passive pixel addressing of the sensor is thus performed.

Such a sensor is described in French patent application no. 16 57391 , mentioned in the introduction.

The terms "line" and "column" can be exchanged, which would correspond to a simple 90 ° rotation of the sensor.

• un étage 320 d'électrodes de collecte de charges, recevant les macro-électrodes de collecte de charge 321 ;
• un étage 330 comprenant un matériau pyroélectrique, identique à celui décrit en référence aux figures 1A et 1B ;
• un étage 340 de blindage électromagnétique, identique à celui décrit en référence aux figures 2A et 2B ;
• une couche 360 d'isolation électrique, telle que décrite en référence aux figures 1A et 1B ;
• un étage 370 dit étage de chauffage, recevant les bandes de chauffage 371; et
• une couche de protection 380, telle que décrite en référence aux figures 1A et 1B.

In the embodiment of Figures 3A and 3B , the thermal pattern sensor 300 comprises, superimposed in this order, above the substrate 310:

• a stage 320 of charge collection electrodes receiving the charge collection macroelectrodes 321;
• a stage 330 comprising a pyroelectric material, identical to that described with reference to Figures 1A and 1B ;
• a stage 340 of electromagnetic shielding, identical to that described with reference to Figures 2A and 2B ;
• a layer 360 of electrical insulation, as described with reference to Figures 1A and 1B ;
• a stage 370 called heating stage, receiving the heating strips 371; and
• a protective layer 380, as described with reference to Figures 1A and 1B .

The contact surface 381 of the sensor is formed here by an upper face of the protective layer 380, on the side opposite the substrate 310.

The charge collection electrode stage 320 is similar to that described with reference to FIGS. Figures 1A and 1B except that the charge collection electrodes of the same column of pixels are formed together in one piece. They are distributed, along the axis (Ox), in a distribution pitch less than or equal to 150 microns, for example 90 microns, or 80 microns, or 50.8 microns.

The heating strips 371 of the heating stage 370 are distributed, along the axis (Oy), preferably in a distribution pitch identical to the distribution pitch of the charge collection macroelectrodes 321. In any case , the heating bands of the stage 370 are preferably distributed in a pitch less than or equal to 150 microns, for example 90 microns, or 80 microns, or 50.8 microns. The heating strips 371 preferably comprise a metal, for example gold or silver.

Each pixel of the pixel matrix is laterally delimited by the intersection between a charge collection macroelectrode 321 and a heating band 371. In other words, each pixel is delimited laterally in planes parallel to the plane of the substrate, by the contours of the intersection between the orthogonal projection, in such a plane, of a macro-charge-collecting electrode 321, and the orthogonal projection, in this same plane, of a heating band 371 .

Each pixel 30 receives a single pad 342 of the electromagnetic shielding stage 340. This stud therefore extends, in the electromagnetic shielding stage 340, through an intersection region located in a plane parallel to the plane of the substrate, at the intersection between an orthogonal projection of a macro-electrode 321 and a orthogonal projection of a heating strip 371.

The figure 3C illustrates a variant 300 ', which differs from the embodiment of the Figures 3A and 3B in that the electromagnetic shielding stage extends above the heating stage.

• l'étage 320' d'électrodes de collecte de charges ;
• l'étage 330' comprenant un matériau pyroélectrique ;
• l'étage de chauffage 370' ;
• la couche 360' d'isolation électrique ;
• l'étage 340' de blindage électromagnétique ; et
• la couche de protection 380' telle que décrite ci-avant, distincte de l'étage 340' de blindage électromagnétique.

In particular, the thermal pattern sensor 300 'comprises, superimposed in this order above the substrate 310':

• the stage 320 'of charge collection electrodes;
• stage 330 'comprising a pyroelectric material;
• the heating stage 370 ';
• the 360 'layer of electrical insulation;
• the stage 340 'of electromagnetic shielding; and
• the protective layer 380 'as described above, distinct from the stage 340' of electromagnetic shielding.

According to this variant, each heating line of the heating stage 370 'also forms a reference electrode, common to all the pixels of a row of pixels of the pixel matrix. Said heating line is adapted to be connected to a source of potential, itself adapted to circulate a non-zero current in the heating line. This current must remain constant during the reading of the loads on the charge collection electrodes of the associated pixels. When the other side of the heating line is connected to ground, said source of potential advantageously alternates between two constant values: a zero value where the heating line does not heat, and a non-zero value where the heating line provides heating by Joule effect.

In a variant, the heating stage 370 'comprises pairs of two strips parallel to each other, one dedicated to heating a line of pixels, and the other forming a common reference electrode for the pixels of the same line. pixels.

According to another variant, the electromagnetic shielding stage does not comprise thermally conductive pads.

According to non-represented variants of the embodiment of the Figures 3A and 3B , and the embodiment of the figure 3C , the charge collection electrodes of the same column of pixels are not interconnected, and the addressing of the pixels is of the active type and requires selection means in each pixel, such as transistors.

According to non-represented variants of the embodiment of the Figures 3A and 3B , and the embodiment of the figure 3C the composite material in the electromagnetic shielding stage 340, or 340 ', further comprises graphene particles.

The invention is not limited to the examples described above, and many variants can be implemented without departing from the scope of the invention.

In particular, the invention applies to any type of thermal sensor comprising a matrix of pyroelectric capacitors, with or without heating elements, with separate heating elements or arranged in heating strips parallel to each other.

In the above examples, the elongated electrically conductive structures of the shielding layer are metal nanowires. In addition or alternatively, it may be nanotubes, in particular carbon nanotubes.

According to a variant of the invention, said elongated electrically conductive structures do not extend in an agglomerate such as a polymeric host matrix, but are entangled with each other and surrounded by a gas such as air forming the medium. surrounding according to the invention. The surrounding environment being then electrically non-conductive, the elongated electrically conductive structures then extend into a pierced network.

The invention applies more particularly to sensors in which a distance between the contact surface and the plane of the upper faces of the lower electrodes of the pyroelectric capacitors, and less than or equal to the pixel pitch of the sensor.

The thermal pattern sensor according to the invention may comprise heating elements which are not interconnected along heating lines.

The invention is also not limited to active type detection, and also covers sensors suitable for passive type detection, without heating element for heating the pyroelectric material portions of the sensor pixels.

When the pixel dimensions permit, each pixel of the pixel matrix may comprise a plurality of pads of the electromagnetic shielding stage.

In all embodiments, the electromagnetic shielding stage extends between the stage comprising a pyroelectric material and the contact surface of the sensor. However, intermediate stages can be located between the electromagnetic shielding stage and the stage comprising a pyroelectric material, respectively between the electromagnetic shielding stage and the contact surface. In particular, a protective layer advantageously extends between the electromagnetic shielding stage and the contact surface, distinct from the electromagnetic shielding stage. In any case, a protective layer forms a layer distinct from the electromagnetic shielding stage.

Preferably, the electromagnetic shielding stage consists entirely of the shielding layer of composite material as described above, or of an assembly comprising thermally conductive pads and said shielding layer.

The sensor may include at least one read circuit, for measuring a quantity of charges collected by a charge collection electrode, and, if necessary, at least one heating control circuit, for sending electrical signals enabling heat the sensor pixels through the heating elements. It may further comprise an electronic processing circuit suitable for constructing an image overall of a thermal pattern, from measurements made at each pixel of the sensor.

The thermal pattern that can be imaged by the sensor may be a papillary impression, or any other pattern associated with an object having a thermal capacity and a specific heat.

• dépôt, directement sur l'étage comportant un matériau pyroélectrique ou sur une couche au-dessus de l'étage comportant un matériau pyroélectrique, d'une encre comportant, en suspension dans un solvant, des nanofils métalliques, des particules du matériau de l'agglomérant, et le cas échéant des particules de graphène ; puis
• évacuation du solvant, pour former la couche de blindage en matériau composite.

A method of manufacturing the electromagnetic shielding stage may comprise the following steps:

• depositing, directly on the stage comprising a pyroelectric material or on a layer above the stage comprising a pyroelectric material, an ink comprising, in suspension in a solvent, metallic nanowires, particles of the material of the agglomerating and, where appropriate, graphene particles; then
• evacuation of the solvent, to form the shielding layer of composite material.

In this case, the composition of the composite material, given above using percentages by weight, corresponds to the composition of the ink after removal of the solvent.

Alternatively, the ink comprises only metal nanowires, suspended in a solvent. After evacuation of the solvent, only the metallic nanowires remain.

Where appropriate, spaces between the metal nanowires are subsequently filled by the material of a layer deposited subsequently above the metal nanowires, for example the material of an electrical insulation layer. Alternatively, the material of a layer then deposited above the metal nanowires fails to fit between the nanowires, so that the nanowires remain surrounded by a gas such as air.

The solvent is chosen so as not to dissolve the layer on which the ink is deposited, for example so as not to dissolve a layer comprising a pyroelectric material.

It is for example a solvent which does not dissolve PVDF and which dissolves polystyrene (agglomerating agent), such as butyl acetate, propyl acetate or PGMEA (propylene glycol methyl ether acetate).

Alternatively, it may be a solvent which does not dissolve the PVDF and which dissolves the PMMA (binder), such as 2-methoxyethanol, butyl acetate, ethoxyethanol, ethyl acetate, propyl acetate, or the PGMEA.

Alternatively, it may be a solvent that does not dissolve the PVDF and dissolves the PEDOT: PSS or PAni (binder), such as water.

The ink is deposited to extend in one piece and without opening above the substrate.

The ink is deposited by a printing technique such as screen printing, inkjet printing, rotogravure, flexo-engraving, offset etching, etc.

Where appropriate, pads of thermally conductive material are formed above the stage comprising a pyroelectric material, before said step of depositing the ink. The pads can also be made by depositing an ink.

As a variant, the ink comprises nanotubes, in particular carbon nanotubes, in addition to or in place of the metal nanowires.

Claims (15)

Thermal pattern sensor (100; 100 ';200;200';300; 300 ') having a matrix of pixels, each pixel having at least one pyroelectric capacitance formed by a pyroelectric material portion disposed between a so-called charges (121) and a so-called reference electrode, and the matrix of pixels comprising, superposed above a substrate (110; 210; 310; 310 '): a stage (120; 320; 320 ') of charge collection electrodes comprising the charge collection electrodes of each of the pixels; and a stage (130; 330; 330 ') comprising a pyroelectric material, comprising the pyroelectric material portions of each of the pixels; the pixel array further comprising an electrically conductive electromagnetic shielding stage (140; 240; 340; 340 ') located between the stage (130; 330; 330') comprising a pyroelectric material and a contact surface ( 181; 381) to apply an object to be imaged;
characterized in that the electromagnetic shielding stage (140; 240; 340; 340 ') comprises a shielding layer (141; 141'; 241) which comprises nanowires and / or nanotubes (1411; 2411) embedded in a medium called the surrounding medium, said nanowires and / or nanotubes being each constituted of a material having a thermal conductivity greater than that of said surrounding medium, and in that a ratio between a distribution pitch (P) of the pixels of the pixel matrix and a thickness (H) of the shielding layer (141; 141 '; 241) is greater than or equal to 20. Thermal pattern sensor (100; 100 ';200;200';300; 300 ') according to claim 1, characterized in that the material of the nanowires and / or nanotubes (1411; 2411) has a thermal conductivity at least ten times greater than that of said surrounding medium (1412; 2412). Thermal pattern sensor (100; 100 ';200;200';300; 300 ') according to claim 1 or 2, characterized in that the shielding layer (141; 141'; 241) consists of a composite material , the composite material comprising said nanowires and / or nanotubes (1411; 2411) integrated in an agglomerate (1412; 2412) which forms said surrounding medium. Thermal pattern sensor (100; 100; 200; 200; 300; 300 ') according to claim 3, characterized in that the composite material comprises between 20% and 40% by weight of nanowires and / or nanotubes (1411; 2411). Thermal pattern sensor (100; 100 ';200;200';300; 300 ') according to claim 3 or 4, characterized in that the binder (1412; 2412) is an electrically insulating polymer matrix, and in that the nanowires and / or nanotubes (1411; 2411) together form a perforated network. Thermal pattern sensor (100; 100 ';200;200';300; 300 ') according to claim 3 or 4, characterized in that the binder (1412; 2412) is an electrically conductive polymer matrix, and in that the nanowires and / or nanotubes (1411; 2411) together form a non-perforated network. Thermal pattern sensor (100; 100 ';200;200';300; 300 ') according to any one of Claims 1 to 6, characterized in that the nanowires and / or nanotubes (1411; 2411) each have a length strictly less than the pixel pitch (P) of the pixel array. Thermal pattern sensor (100 ';200') according to any one of claims 3 to 7, characterized in that the composite material further comprises graphene particles (1413; 2413). Thermal pattern sensor (100 ';200') according to claim 8, characterized in that the composite material further comprises between 10% and 30% by weight of graphene particles (1413; 2413). Thermal pattern sensor (200; 200 ';300;300') according to any one of claims 1 to 9, characterized in that the electromagnetic shielding stage (240; 340; 340 ') further comprises pads ( 242; 342) having graphene or metal. Thermal pattern sensor (300; 300 ') according to one of Claims 1 to 10, characterized in that : each pixel furthermore comprises a heating element capable of heating, by Joule effect, the portion of pyroelectric material of said pixel; and a heating stage (370; 370 '), comprising the heating elements of each of the pixels, extends in the matrix of pixels between the stage comprising a pyroelectric material (330; 330') and the contact surface ( 381). Thermal pattern sensor (300; 300 ') according to claim 11, characterized in that : - The heating elements of the same pixel line are formed together in one piece, in the same heating band (371); the charge collection electrodes of the same column of pixels are formed together in one piece, in the same load collection macro-electrode (321); and the electromagnetic shielding stage (340; 340 ') further comprises a matrix of studs (342) comprising graphene or metal, each stud (342) extending through a region of intersection between a projection of a heating band (371) and a projection of a charge collection macro-electrode (321), said projections being orthogonal projections in a plane parallel to an upper or lower face of the substrate (310; 310 '). Thermal pattern sensor (300) according to claim 11 or 12, characterized in that the matrix of pixels comprises, superimposed: the charge collection electrode stage (320); the stage comprising a pyroelectric material (330); the electromagnetic shielding stage (340), further forming the reference electrodes of the pixels of the pixel matrix; an electrical insulation layer (360); and the heating stage (370). Thermal pattern sensor (300 ') according to claim 11 or 12, characterized in that the matrix of pixels comprises, superimposed: the charge collection electrode stage (320 '); the stage comprising a pyroelectric material (330 '); the heating stage (370 '), the heating elements also forming the reference electrodes of the pixels of the pixel matrix; an electrical insulation layer (360 '); and the electromagnetic shielding stage (340 '). A method of manufacturing the pixel array of a thermal pattern sensor (100; 100 ';200;200';300; 300 ') according to any one of claims 1 to 14, characterized in that a step of embodiment of the electromagnetic shielding stage (140; 240; 340; 340 ') comprises a deposition of an ink comprising, in suspension in a solvent, said nanowires and / or nanotubes (1411; 2411).

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